In multi-phase electronic converter applications, a number of bridge driver circuits (full or half) can be cascaded together while sharing a common power supply 110. A full bridge converter 100 is shown in FIG. 1 with four actuators (120) cascaded together. In this design, each load element 120 (actuator) is independently controlled by modulating the conduction of the appropriate power devices, in one of the three voltage operating modes (positive voltage, negative voltage, free-wheeling mode) by actuating switches 112 and 118, 114 and 116, 112 and 116 or 114 and 118, respectively.
A half-bridge equivalent configuration can also be used for applications that do not require bi-directional current flow, shown in FIG. 2. One difference between the two is that the half bridge circuit 200 has two of the power switches (114 and 116) replaced with power diodes (122 and 124, respectively). This substitution provides a cost reduction by eliminating the power switches as well as the associated gate drive circuitry and controller complexity.
Either type of converter can be used for controlling actuators and are representative of the majority of power converters that can be used.
However, the inventors herein have recognized a disadvantage when trying to use such converter designs to control electromechanically actuated valves of a cylinder in an internal combustion engine. For example, in the case of a half bridge converter, four power devices (2 switches and 2 diodes) are required for each electromagnet. And, since electrically actuated valves of an engine typically use two actuator coils per cylinder, a typical 32 valve V-8 engine would require 256 devices. This creates a significant added cost for an engine with electromechanically actuated valves, even if not all valves are electrically powered. Further, not only would the above converter approaches require significant numbers of devices, but would also increase wiring and harness costs, since two wires are required per actuator coil.
To overcome the above drawbacks, the inventors herein have developed a power converter that utilizes a split capacitor power supply in various different forms. By using such a converter topology, along with appropriate positioning of flyback diodes and switches, it is possible to require only a single switch to actuate each coil (although more can be used if desired).
However, the above configuration can result in unbalanced capacitor voltages depending on the actuation and loading of the different actuators. This can result in inconsistent actuation of the coils, and when used to control valves of an engine, variations in engine output or air-fuel ratio, for example.
One approach to regulate a voltage of a circuit used for valves of an engine is described in EP 1 010 867. However, the inventors herein have recognized several disadvantages with such an approach. For, the approach of EP '867 utilizes separate actuation and switches to perform the voltage regulation, thereby adding cost to the power converter system.
The above disadvantages can be overcome by a system comprising:                a circuit for selectively actuating an electromechanical actuator coupled to a valve of an engine, the circuit having at least one energy storage device and at least one switch that selectively energizes said actuator; and        a computer readable storage medium having a computer program encoded therein for regulating energy stored in said energy storage device, said computer storage medium comprising:        code for regulating voltage at said energy storage device by adjusting said switch during a first set of engine valve operating conditions.        
In this way, it is possible to have a system that enables efficient actuation of the cylinder valves that is capable of operation even under conditions where different cylinder valves experience different loading conditions, such as an intake valve and an exhaust valve, or the opening versus closing of a single valve.